U.S. Pat. No. 7,781,224 issued Aug. 24, 2001 to Sue I. Martin et al titled “Safe Biodegradable Fluorescent Particles,” assigned to Lawrence Livermore, National Security, LLC., provides the following state of technology information:                The present invention provides a “safe” fluorescent particle for a variety of applications. The particle comprises a non-biological, biodegradable carrier and natural fluorophores encapsulated in the non-biological, biodegradable carrier. In some embodiments the particle is used as a simulant for mimicking the fluorescence properties of microorganisms. However, the particle need not mimic the fluorescent characteristics of a microorganism, rather it can be incorporated into one or more natural fluorophores as a means for fluorescence detection. Single or combinations of fluorophores are encapsulated to produce a desired fluorescent effect such as particles that fluoresce at 370 nm maxima. The particles can therefore be tuned to the excitation wavelength of a fluorescence detector.        One application for these particles is their use in aerosol studies, such as large scale air dispersal to track particulate migration over vast areas, or for urban particle dispersion studies. Currently, researchers performing these studies rely on air dispersion models and gas tracer tests to determine the movement and flow of aerosols in urban environments such as in cities—around and through occupied buildings—because “safe” particles are not available. These particles would provide those safety benefits. Furthermore, these particles could be designed with the appropriate density and perhaps shape of a microorganism to mimic the aerodynamic movement of a microorganism.        An example of aerosol study is described in the article, “An examination of the urban dispersion curves derived from the St. Louis dispersion study” by Akula Venkatram in Atmospheric Environment 39 (2005) 3813-3822, which describes the St. Louis study conducted over the period 1963-1965. The study consisted of a series of 26 daytime and 16 evening experiments in which fluorescent zinc cadmium sulfide particles were released near ground level at two different locations under a variety of meteorological conditions. During the first year of the experiments, the release was at ground level in a relatively open area in a park located west of the downtown area. In the second year, the tracer was released from the top of a three-story building surrounded by trees and similar buildings. The main downtown area, consisting of buildings with an average height of 40 m, was about 5 km away from both release locations.” The disclosure of the article, “An examination of the urban dispersion curves derived from the St. Louis dispersion study” by Akula Venkatram in Atmospheric Environment 39 (2005) 3813-3822 is incorporated herein by this reference.        Another example of aerosol study is described in the article, “Use of Salt Lake City URBAN 2000 Field Data to Evaluate the Urban Hazard Prediction Assessment Capability (HPAC) Dispersion Model” by Joseph c. Chang in Journal Of Applied Meteorology pages 485-501 (2005), which provides the following background about the study: “The potential impacts of the atmospheric release of chemical, biological, radiological, and nuclear (CBRN) or other hazardous materials are of increasing concern. Hazardous releases can occur due to accidents, such as the release of toxic industrial chemicals in Bhopal, India, in 1984 (e.g., Sharan et al. 1996) and the Chernobyl nuclear power plant disaster in the Ukraine in 1986 (e.g., Puhakka et al. 1990). They can also occur as an unintentional result of military actions, such as the U.S. destruction of rockets with chemical warheads at Khamisiyah, Iraq, after the 1991 Gulf War (Winkenwerder 2002). More recently, terrorist incidents in urban settings, such as the events on 11 Sep. 2001 in New York City, N.Y., and Washington, D.C., and military conflicts dramatically raise concerns for the possibility of mass casualties.” The disclosure of the article, “Use of Salt Lake City URBAN 2000 Field Data to Evaluate the Urban Hazard Prediction Assessment Capability (HPAC) Dispersion Model” by Joseph c. Chang in Journal Of Applied Meteorology pages 485-501 (2005) is incorporated herein by this reference.        